Riveted fastener extraction apparatus and method

ABSTRACT

An extraction apparatus ( 40 ) for the removal of a riveted fastener ( 12 ) from a structure ( 10 ) includes a shaft ( 42 ) and a cutting element ( 62 ). The cutting element ( 62 ) is mechanically coupled to the shaft ( 42 ) and is configured to cut a portion of the riveted fastener ( 12 ). The shaft ( 42 ) and the cutting element ( 62 ) are configured for insertion through an inner channel ( 24 ) of the riveted fastener ( 12 ). A method of replacing the riveted fastener ( 12 ) from the structure ( 10 ) includes inserting the extraction apparatus ( 40 ) through the inner channel ( 24 ). The extraction apparatus ( 40 ) is rotated. A portion of the riveted fastener ( 12 ) that extends through the structure ( 10 ) is removed. A head ( 20 ) of the riveted fastener ( 12 ) is also removed from the structure.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of co-pending U.S. application Ser.No. 10/907,129, filed Mar. 22, 2005.

GOVERNMENT CONTRACT

The invention described herein was made in the performance of work withGovernment support under Contract No. HP10926M8S. The Government hascertain rights in this invention.

TECHNICAL FIELD

The present invention is related generally to riveted fasteners. Moreparticularly, the present invention is related to a method of extractinga riveted fastener and to apparatuses used to perform such extraction.

BACKGROUND OF THE INVENTION

There are many situations where it is required to provide a structure orthe like with captive nuts such that a system can be assembled in placeand/or such that components may be fastened to the structure. To satisfythis need blind rivet nuts, commonly referred to as “rivnuts”, are oftenused and installed into a structure. This is especially true insituations where access to only one side of the structure is accessible.The inaccessible side may be referred to as or associated with a blindcavity.

A structure is typically preformed or drilled to have designated holesfor the insertion of the rivnuts. The rivnuts are subsequentlycompressed using a mandrel or other rivnut installation tool such thatthey are crimped intimately around the periphery of designated holes,thus preventing withdrawal therefrom. In general, rivnuts have an innerthreaded channel for the coupling of a threaded fastener, such as a boltor screw, therein and thus the attachment of components thereon.

Rivnuts are often used, for example, on gyro structures includingstabilized platform gimbal assemblies, which have blind inner cavities.The stated rivnuts are utilized for the attachment of wire harnesses tothe gimbal assemblies. During certain maintenance, repair, modification,or update tasks of the gyro structures the wire harnesses are removedfrom the gimbal assemblies.

The wire harnesses are attached via cable clamps to the gimbals. Theclamps are attached using screws. A locking compound, such as LOCKTITE®,is often applied to the screws prior to being threaded into the rivnutsto prevent loosening or dislodging of the screws. After an extendedperiod of time and due to the use of the locking compound, when thescrews are removed the threads within the rivnuts can be stripped ordamaged. In certain instances, the removal of the screws causes therivnuts to loosen relative to the structure and spin in the associatedstructure holes.

Spare gimbals for the replacement of the gimbals, that have one or moredamaged rivnuts, are often scarce or nonexistant. Thus, the entire gyroassociated stabilized platforms are unuseable and non-serviceable.Replacement of gimbals with newly manufactured gimbals is generallyconsidered an undesirable option due to the high costs, part complexityof a gyro stabilized platform, and many times the lack of originalmanufacturing tooling associated with the gimbals.

It is also undesirable to drill out a rivnut. When drilling out a rivnutthe lower inner portion of the rivnut breaks off and then resides withinand cannot be removed from the blind cavity. The broken off portion isconsidered foreign object debris and can rattle within the cavity andcause noise or improper operation of gyro components.

Thus, there exists a need for an improved removal technique that allowsfor the extraction of a rivnut including the portion thereof thatresides within a blind cavity.

SUMMARY OF THE INVENTION

One embodiment of the present invention provides an extraction apparatusfor the removal of a riveted fastener from a structure. The apparatusincludes a shaft and a cutting element. The cutting element ismechanically coupled to the shaft and is configured to cut a portion ofthe riveted fastener. The shaft and the cutting element are configuredfor insertion through an inner channel of the riveted fastener.

Another embodiment of the present invention provides a method ofreplacing a riveted fastener from a structure. The method includesinserting an extraction apparatus, having a cutting element, through aninner channel of the riveted fastener. The extraction apparatus isrotated. A portion of the riveted fastener that extends through thestructure is removed. A head of the riveted fastener is also removedfrom the structure.

The embodiments of the present invention provide several advantages. Onesuch advantage is the provision of extraction apparatuses for theremoval of riveted fasteners. The apparatuses allow for the removal ofriveted fasteners without portions of the riveted fasteners remainingwithin associated blind cavities.

Another advantage provided by an embodiment of the present invention, isthe provision of a method of removing essentially the entire rivetedfastener from a structure having a blind cavity. This allows for thereplacement of rivnuts and the reuse and nonreplacement of gyrostabilized platform gimbals.

Still another advantage provided by an embodiment of the presentinvention, is the nondestructive provision of removing a rivetedfastener without cutting into or damaging the mounting structure of thatfastener. This can improve safety associated with the removal of, forexample, rivnuts from a beryllium gyro gimbal.

Furthermore, the above-stated advantages reduce operating costs throughreuse of gyro gimbals and eliminate the desire and/or requirementassociated with the replacement of gimbals due to one or more damagedrivnuts.

Other features, benefits and advantages of the present invention willbecome apparent from the following description of the invention, whenviewed in accordance with the attached drawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a gyro stabilized platform gimbal havingriveted fasteners;

FIG. 2A is a top view of a rivnut prior to installation;

FIG. 2B is a cross-sectional side view of the rivnut of FIG. 2A;

FIG. 2C is a cross-sectional side view of the rivnut of FIG. 2Asubsequent to installation;

FIG. 3 is a perspective view of an extraction cutting apparatus inaccordance with an embodiment of the present invention;

FIG. 4 is a cross-sectional perspective view of the extraction cuttingapparatus of FIG. 3 inserted through a rivnut and into a blind cavity ofa gyro gimbal in accordance with an embodiment of the present invention;

FIG. 5 is a close-up cross sectional perspective view of the extractioncutting apparatus subsequent to the cutting of the rivnut in accordancewith an embodiment of the present invention;

FIG. 6 is a perspective view of a riveted fastener head extractionapparatus in accordance with an embodiment of the present invention;

FIG. 7 is a side view of a blind riveted fastener depth indicator inaccordance with an embodiment of the present invention;

FIG. 8 is a logic flow diagram illustrating a method of replacing ariveted fastener in accordance with an embodiment of the presentinvention;

FIG. 9 is a perspective view of a gyro gimbal mounted on a millingmachine;

FIG. 10 is a perspective view of a test indicator residing between themilling machine and the gyro gimbal of FIG. 9 and used in accordancewith an embodiment of the present invention;

FIG. 11 is a perspective view of a reamer mounted within a chuck of themilling machine and used in accordance with an embodiment of the presentinvention;

FIG. 12 is a perspective view of a travel indicator and the blindriveted fastener depth indicator residing between the milling machineand a riveted fastener and used in accordance with an embodiment of thepresent invention;

FIG. 13 is a perspective view of the riveted fastener head extractionapparatus illustrating removal of the riveted fastener in accordancewith an embodiment of the present invention;

FIG. 14 is a perspective view illustrating extraction of debris from ablind cavity in accordance with an embodiment of the present invention;and

FIG. 15 is a perspective view of a fiber optic system for inspecting theblind cavity subsequent to removal of the riveted fastener in accordancewith an embodiment of the present invention.

DETAILED DESCRIPTION

In the following Figures the same reference numerals will be used torefer to the same components. While the present invention is describedprimarily with respect to a method of extracting a riveted fastener andto apparatuses used to perform such extraction, the present inventionmay be adapted and applied in various fastener removal and replacementapplications. The present invention may be applied in aeronauticalapplications, nautical applications, railway applications, automotivevehicle applications, and commercial and residential applications. Also,a variety of other embodiments are contemplated having differentcombinations of the below described features of the present invention,having features other than those described herein, or even lacking oneor more of those features. As such, it is understood that the inventioncan be carried out in various other suitable modes.

In the following description, various operating parameters andcomponents are described for one or more constructed embodiments. Thesespecific parameters and components are included as examples and are notmeant to be limiting.

Also, although the present invention is primarily described with respectto the removal and replacement of rivnuts, the present invention may beapplied to other riveted fasteners known in the art. For example, thepresent invention may be applied to captive nuts or nut plates.

Referring now to FIG. 1, a perspective view of a gyro stabilizedplatform gimbal 10 having riveted fasteners 12 is shown. The rivetedfasteners 12 are shown as rivet nuts or rivnuts and are utilized toattach wire harness cable clamps and thread screws (both of which notshown) thereon. The gyro gimbal 10 has a first half 14 and a second half16 that are mated together. The halves 14 and 16 may be cemented to eachother to form a single solid element. Upon cementing of the halves 14and 16 the riveted fasteners 12 are only accessible from the exterior ofthe gyro gimbal 10.

Referring now to FIGS. 2A-C, a top view and a cross-sectional side viewof one of the rivnuts 12 prior to installation and a cross-sectionalside view of one of the rivnuts 12 subsequent to installation are shown.The rivnut 12 has a head 20 and a tubular section 22 with an innerchannel 24. The inner channel 24 may be threaded. The rivnut may alsoinclude a key 26. The tubular section 22 is inserted and extendedthrough the structure 28. Upon insertion, the tubular section 22includes a structure laterally adjacent portion 30, which extendsthrough the hole 31 of the structure 28, and a prior-protruding portion(not shown). The prior-protruding portion refers to the protrudingportion of the rivnut 12 prior to compression thereof. Upon installationof the rivnut 12, the tubular section 22 includes the adjacent portion30 and the post-protruding portion 32, which includes a compressed area34. When installed, part of the prior-protruding portion of the tubularsection 22 is compressed, which locks the rivnut 12 to the structure 28and forms the compressed area 34. The rivnut 12 may be installed usingany conventional method of installation.

Referring now to FIG. 3, a perspective view of a riveted fastenerextraction cutting apparatus 40 in accordance with an embodiment of thepresent invention is shown. The cutting apparatus 40 includes a shaft42, with a top surface 43, and a pivot plate 44. The shaft 42 includes afirst tubular section 46, a shoulder 48, and a second tubular section50. The first section 46 has a first outer diameter D1 and the secondsection 50 has a second outer diameter D2 that is smaller than the firstdiameter D1. Although the shaft 42 is shown as having multiple tubularsection with multiple outer diameters, it may have a single tubularsection with a single outer diameter. The first section 46 is configuredfor insertion into a high-speed rotating device, such as a chuck of adrill or other rotating device, for rotation of the cutting apparatus40. The second section 50 is configured for insertion within an innerchannel of a riveted fastener, such as the inner channel 24. The secondsection 50 includes a slot 52 that extends along a center plane,designated by line 54, of the shaft 42 from an insertion end 56 inward afirst predetermined distance D3. The pivot plate 44 is coupled to thesecond section 50. A center portion 58 of the pivot plate 44 resideswithin the slot 52 and is coupled to the shaft 42 via a pivot pin 60.The pivot plate 44 is free to rotate about the pivot pin 60.

The pivot plate 44 includes one or more cutting elements 62, each with apair of cutting edges 64, and a pendulous weight 66. During insertionand removal of the second section 50 in and out of a riveted fastener,the pivot plate 44 is in-line or parallel with the shaft 42 and thecutting element 62, opposite the pendulous weight 66, is within the slot52. When the second section 50 is not rotating the gravitational forcesexerted on the pivot plate 44, due to the pendulous weight 66, cause thepivot plate 44 to rotate to the parallel orientation. During use androtation of the cutting apparatus 40 the pivot plate 44 rotates suchthat the cutting elements 62 and the pendulous weight 66 pivot outwardlyand are perpendicular to a centerline and center axis of rotation 68 ofthe shaft 42. Rotation of the cutting apparatus 40 is shown by arrow 70.The cutting elements 62 may be integrally formed as part of the pivotplate 44 or separate therefrom. The ends and/or edges of the pivot plate44 may be sharpened to form the cutting elements 62.

In operation, the second section 50 is inserted in and protrudes througha riveted fastener such that the pivot plate 44 is free to rotateexternally from the fastener. When the second section 50 is rotated thecutting elements 62 are pivoted outward due to the centrifugal forcesexerted thereon. As such, the cutting edges 64 are perpendicular to thecenter axis 68 to allow for the cutting of the riveted fastener.

The shaft 42 may be formed of a nonmagnetic material such that duringrotation of the shaft 42 and cutting of a riveted fastener the shaft 42does not become magnetized. A magnetized shaft can attract and preventfree rotation of the pivot plate 44. The shaft 42 may be formed of, forexample, stainless steel, titanium, plastic, or other nonmagneticmaterial.

The cutting elements 62 may be used to machine or cut, which includesgrinding, portions of riveted fasteners. The cutting elements 62 may beformed of high-speed steel, carbide, or other cutting material known inthe art. The pivot plate 44 may be formed of the same or differentmaterial as that of the cutting elements 62. High-speed steel generallyrefers to a combination of one or more materials selected from tungsten,molybdenum, vanadium, and cobalt. Carbide may include tungsten carbide,silicon carbide, ceramics, or the like. Also, although the pivot plate44 is shown as having a single cutting element, any number of cuttingelements may be used.

Referring now to FIG. 4, a cross-sectional perspective view of theextraction cutting apparatus 40 inserted through one of the rivnuts 12and into a blind cavity 72 of the gyro gimbal 10 in accordance with anembodiment of the present invention is shown. Prior to rotation of theshaft 42 the second section 50 is inserted into and through the rivnut12. The second section 50 may be inserted up to the shoulder 48 abutsthe head 20, as shown, or to a lesser extent as desired. The secondsection 50 is inserted through the rivnut 12 at least until the pivotplate 44 is able to rotate freely. After full protrusion of the pivotplate 44 the shaft 42 may be rotated and lifted to cut away theprotruding portion 32 including at least partially the compressed area34.

Referring now to FIG. 5, a close-up cross sectional perspective view ofthe cutting apparatus 40 subsequent to the cutting of the rivnut 12 inaccordance with an embodiment of the present invention is shown. Noticethat a thin protruding remainder 74, having a cut surface 75, is leftafter cutting away a majority of the protruding portion 32. In certainapplications, such as when removing a rivnut from a gyro gimbal, thecutting apparatus 40 is halted prior to coming in contact with an innersurface 76 of the gimbal 10. This prevents damage to the gimbal 10 andprevents cutting into a material, such as beryllium. This process isdescribed in further detail below.

Referring now to FIG. 6, a perspective view of a riveted fastener headextraction apparatus 78 in accordance with an embodiment of the presentinvention is shown. The head extraction apparatus 78 is used to remove ariveted fastener from a structure, such as from the gimbal 10 or thestructure 28, after cutting a protruding portion of the rivetedfastener, such as the protruding portion 32. The head extractionapparatus 78 includes a fastener 80 and a support element 82. Thefastener 80 is configured for insertion into at least the head of ariveted fastener. The support member 82 is coupled to the fastener 80and is configured for positioning over a riveted fastener head. Thesupport member 82 has an open sided and ended tubular slot 84 with aninner diameter D4 that is larger than the outer diameter of a rivetedfastener head. During use of the head extraction apparatus 78, legs 86of the support member 82 are positioned proximate and on opposite sidesof a riveted fastener head and the protruding remainder portion. Thefastener 80 is threaded and is turned into the riveted fastener head.Rotation of the fastener 80 within the support element 82 and into theriveted fastener head causes the head to be pulled out of thecorresponding structure. This is described in step 170 below.

Referring now to FIG. 7, a side view of a blind riveted fastener depthindicator 88 in accordance with an embodiment of the present inventionis shown. The depth indicator 88 includes an adaptor 89, with a handle90 and a body 92, and a depth hook 94. The handle 90 is configured forinsertion into a measuring device, for example, into a chuck of amilling machine having a travel indicator. The handle 90 may bethreaded. The body 92 is attached to the handle 90 and includes asetscrew 93 for insertion and removal of the depth hook 94. The handle90, the body 92, and the depth hook 94 are sized and configured forinsertion within a riveted fastener. The handle 90, the body 92, and thedepth hook 94 may be formed of similar materials and may be formed as asingle integral unit or as separate components, as shown. The handle 90,the body 92, and the depth hook 94 may be generally cylindrical inshape, as shown, or may be of other shapes and of various sizes.

The depth hook 94 has a shaft 95, a tapered tip 96, and a return end 97.The tapered tip 96 and the return end 97 are used to determine theprotruding depth of a cut riveted fastener. This is explained in furtherdetail below with respect to the cut verification phase in steps152-168.

Referring now to FIG. 8, a logic flow diagram illustrating a method ofreplacing a riveted fastener in accordance with an embodiment of thepresent invention is shown. Although the following steps are describedwith respect to the replacement of a gyro gimbal rivnut and to the useof a vertical milling machine for the removal of the rivnut, the stepsare for example purposes only and may be easily modified for otherriveted fasteners and removal equipment.

The following steps 100-114 may be referred to as the setup preparationphase. In step 100, the head of a vertical milling machine is properlytramed such that the head and spindle are normal to the milling machinetable using techniques known in the art. In step 102, a readout, whichmay be digital or in the form of a dial indicator, is installed on themilling machine to provide an accurate measurement of the verticaldisplacement of the spindle. A vertical milling machine 101 having atable 103 is shown in FIG. 9.

In step 104, a drill chuck may be installed into the spindle of themilling machine. A drill chuck 105 and a spindle 107 are shown in FIGS.9 and 11. In the following steps, one or more indicators, reamers, taps,and riveted fastener extraction cutting apparatuses are described withrespect to the direct mounting or installing thereof in a drill chuck,these devices may be configured for sleeve and collet installation orfor direct installation into a spindle. The state devices may beconfigured for insertion into a sleeve or a collet prior to installationinto a spindle. Also, the stated devices may be configured for directinstallation within a spindle without the use of a drill chuck, asleeve, or a collet. For example, the shaft 42, or more specifically,the first section 46 of the cutting apparatus 40 may be tapered andsized for insertion into a sleeve prior to installation into a spindleor for direct installation into the spindle.

In step 106, a structure, such as the gyro gimbal 10, is mounted on themilling machine table such that the damaged rivnut of concern to bereplaced is accessible. In step 108, the center of the rivnut isdetermined. A center test indicator, such as the test indicator 107shown in FIG. 10, may be used to determine the rivnut center.

In step 110, the X and Y axes are zeroed on the milling machine. In step112, a mark is placed on the head of the rivnut as a visual aid toindicate if and when the rivnut is rotated. In step 114, a vacuum devicehaving a vacuum nozzle, hose, or the like, such as the vacuum hose 115shown in FIG. 11, may be positioned near the rivnut or point ofoperation. Suction through the hose is activated. The vacuum may remain“ON” during any cutting and reaming operations depending upon theapplication and materials of related components. Use of the vacuum canbe especially desirable when cutting or reaming is performed on a rivnutthat is mounted on a gimbal formed of a material containing beryllium orthe like.

The following steps 116-120 may be referred to as the riveted fastenerpreparation phase. In step 116, the rivnut is reamed. A reamer, such asthe reamer 117 shown in FIG. 11, is installed in the drill chuck andused to ream the inner channel of the rivnut, such as the inner channel24. The set spindle speed for the reaming procedure may vary dependingupon the size of the reamer, the size of the rivnut inner channel, andthe materials of the rivnut and reamer. As an example, when a number 24reamer having a 0.152 inch diameter reamer is used the spindle speed maybe set at approximately 1000RPM.

In step 118, the reamed inner channel is tapped. The rivnut may betapped by hand or manually to thread the reamed inner channel of therivnut. Threading of the reamed inner channel aids further in theremoval of the rivnut head from the gyro gimbal. In step 120, the rivnutis again reamed using the same reamer as used in step 116 to remove anyburrs that may exist due to the tapping process of step 118.

The following steps 122-134 may be referred to as the cuttingpreparation phase. In step 122, a riveted fastener extraction cuttingapparatus, such as the cutting apparatus 40, is installed into the drillchuck. In step 124, a first verification is performed to assure that thepivot plate, such as the pivot plate 44, rotates freely on the cuttingapparatus. In step 126, the pivot plate is rotated and held at aperpendicular or 90° position relative to the centerline of the shaft.

In step 128, with the spindle not rotating, the quill and thus thespindle of the milling machine are lowered such that the pivot platetouches the top surface of the rivnut head. In step 130, the readout ofstep 102 is zeroed.

In step 132, the quill is raised such that the cutting apparatus isabove the rivnut head. At this stage, the pivot plate should rotatefreely and at rest be in a vertical orientation parallel with the shaft.One of the cutting element, such as one of the cutting elements 62, isin the slot of the second section, such as the slot 52 of the secondsection 50.

In step 134, a second verification is performed to assure that the pivotplate rotates freely. The spindle is spun while the cutting apparatus isabove and not contacting the rivnut. The spindle may be spun, as anexample, at a speed of approximately 1800 RPM. When it is clear that thepivot plate is able to rotate freely the spindle is stopped.

The following steps 136-142 may be referred to as the cutting phase. Instep 136, the cutting apparatus is inserted into the rivnut such thatthe pivot plate protrudes through the inner channel. The cuttingapparatus may be inserted up to when the shoulder of the cuttingapparatus, such as the shoulder 48 is approximately 0.05 inches from therivnut head.

In step 138, the milling machine is activated and the spindle isrotated. The spindle may be spun at approximately 1800 RPM. Of course,the speed of the spindle is varied per application.

In step 140, the quill is raised in an upward motion to gently cut outthe protruding portion of the rivnut up to a predetermined dimensionaway from the inner surface of the blind cavity of the gyro gimbal. Forexample, the protruding portion 32 may be cut until one of the cuttingedges 64 or the upper cutting edge thereof is the predetermined distancefrom the inner surface 76. The quill may be raised to a predeterminedsetting Ps, which is equal to the sum of the height of the rivnut headH1, the cross-sectional thickness of the gimbal T, the predetermineddistance Pd, and the height of the cutting element H2. This can bemeasured using the readout. The stated dimensions can be best seen inFIG. 5. The predetermined distance Pd refers to the remaining portion ofthe rivnut that protrudes within the gimbal upon completion of thecutting process. Depending upon the application the cutting apparatusmay start cutting the uncut protruding portion when it is approximatelyat a readout position of 0.59 inches. As an example, the quill mayberaised from the initial cutting position of 0.59 inches to apredetermined setting Ps of 0.275 inches.

In step 142, the cutting apparatus is lowered such that the shoulder iswithin approximately 0.05 inches of the rivnut head and the spindle isstopped from spinning

The following steps 144-150 may be referred to as the cutting apparatusremoval phase. In step 144, the cutting apparatus is released from thespindle. In step 146, the quill and spindle are raised leaving thecutting apparatus extending through the rivnut and the pivot plate inthe blind cavity. In step 148, the top surface, such as the top surface43, of the cutting apparatus shaft is lightly striked in a vertical ordownward direction to assure that the pivot plate is in a verticalposition. The shaft is held and may be striked, for example, with ahandle of a screwdriver or the like. In step 150, the cutting apparatusis removed from the rivnut.

The following steps 152-168 may be referred to as the cut verificationphase. In the cut verification phase the protruding depth of the rivetedfastener or rivnut is measured to assure that it is approximately withina desired or predetermined depth range. An example depth range isapproximately between 0.005-0.01 inches.

In step 152, a displacement indicator is installed in the chuck. Thedisplacement indicator may be in the form of a dial indicator. A sampledisplacement indicator 153 is shown in FIG. 12. In step 154, a blindriveted fastener depth indicator, such as the depth indicator 88, isinstalled in the displacement indicator. Of course, steps 152 and 154may be reversed.

In step 156, the depth indicator is lowered into and through the rivnut.In step 158, the spindle is moved laterally such that the chamfered tip,such as the chamfered tip 96, of the depth indicator is directly belowthe inner surface of the gyro gimbal. In step 160, the depth indicatoris raised until the chamfered tip touches the inner surface. In step162, the displacement indicator is zeroed.

In step 164, the depth indicator is lowered and laterally translatedsuch that the shaft, of the depth indicator is approximately in thecenter of the rivnut. In step 166, the depth indicator is raised untilthe chamfered tip touches the cut surface of the remaining protrudingportion of the rivnut, such as the cut surface 75 of the remainingportion 74.

In step 168, a measurement is taken on the displacement indicator todetermine depth of the remaining protruding portion. When the determineddepth is within the predetermined range step 170 is performed. When thedetermined depth is larger than the depths associated with thepredetermined range then steps 122-166 are repeated to further cut theriveted fastener such that the depth of the protruding portion is withinthe predetermined range.

The following steps 170-176 may be referred to as the clean-up phase. Instep 170, a riveted fastener head extraction apparatus, such as theextraction apparatus 78, is used to remove the head and the remainingportions of the rivnut. The shaft of the extraction apparatus is screwedinto the tapped threads of the head formed in step 118. As the shaft isscrewed into the head the rivnut is pulled out of and separated from thestructure. The rivnut may need to be held from rotating during removal,thus a pair of pliers may be used to hold the head and prevent it fromrotating within the structure. This is illustrated in FIG. 13, wherein apair of pliers 171 are used to hold the rivnut head.

In step 172, a vacuum having a nozzle, hose, or the like, such as thehose 173 that is shown in FIG. 14, is used to remove shavings and debrisfrom the interior of the blind cavity. Tweezers may be used asappropriate to assist in the removal of the debris. Nearby or otherblind cavity holes, other than that in which the rivnut was removedfrom, may need to be plugged to provide adequate negative pressure toremove the debris. Tubing may be attached to the vacuum and insertedinto the blind cavity to further assist in the removal of debris. Smalldiameter nylon tubing may be used. In step 174, the gyro gimbal may beremoved from the table and shaken to loosen any remaining debris. Step172 may be repeated following step 174.

In step 176, a visual debris indication device may be used to verifythat the blind cavity is free of debris. A sample visual debrisindication device 177 is shown in FIG. 15 having a fiber optic cable 179and a light source 181. The visual debris indication device may be inthe form of a fiber optic light to allow one to inspect the interior ofthe blind cavity, as shown. The visual debris installation device mayalso be in the form of a fiber optic camera or may be in some other formknown in the art.

The following steps 178-188 may be referred to as the replacement phase.In step 178, a replacement rivnut is installed. The replacement rivnutis threaded onto a rivnut installation tool and is installed usingtechniques known in the art. In step 180, the head of the replacementrivnut is marked to allow for visual indication of rivnut rotationduring the following torque test of step 184. In step 182, a fastener,having a washer, is screwed into the replacement rivnut.

In step 184, it is determined whether the rivnut is installed properlysuch that it does not rotate under an applied torque. A torque wrenchmay be used to apply rotational force on the fastener of step 182. Atorque pressure is applied within a given range. For example, a torquepressure of approximately between 12-15 in-lbs may be applied. When therivnut does rotate step 186 is performed, otherwise step 188 isperformed.

In step 186, the installation tool may be reused to further compress thereplacement rivnut or the replacement rivnut may be removed as describedabove and another rivnut may be installed. In step 188, the fastener andthe washer are removed from the replacement rivnut and the markingapplied in step 180 may be removed.

The above-described steps are meant to be illustrative examples; thesteps may be performed sequentially, synchronously, simultaneously, orin a different order depending upon the application.

The present invention provides a method for the replacement of rivetedfasteners, that is especially applicable to riveted fastenerapplications where only one side of the riveted fastener is accessibledue to the presence of a blind cavity or the like. The present inventionalso provides sample extraction apparatuses and a sample depth indicatorthat may be used in the stated method. The present invention allows forthe replacement of riveted fasteners via a single access side withoutcutting or damaging associated structures in which the riveted fastenersare installed.

While the invention has been described in connection with one or moreembodiments, it is to be understood that the specific mechanisms andtechniques which have been described are merely illustrative of theprinciples of the invention, numerous modifications may be made to themethods and apparatus described without departing from the spirit andscope of the invention as defined by the appended claims.

1. A method of replacing a riveted fastener that extends through astructure comprising: inserting an extraction apparatus having a cuttingelement through an inner channel of the riveted fastener; rotating saidextraction apparatus; removing at least a portion of the rivetedfastener that extends through the structure; and removing a head of theriveted fastener from the structure.
 2. A method as in claim 1 whereinrotating said extraction apparatus comprises pivoting said cuttingelement outwardly from an axis of rotation.
 3. A method as in claim 1wherein removing at least a portion of the riveted fastener comprises:lifting said extraction apparatus; and cutting said portion.
 4. A methodas in claim 1 wherein removing said head comprises threading a shaftinto said head to separate said head from the structure.
 5. A method asin claim 1 further comprising vacuuming machined elements of saidportion.
 6. A method as in claim 1 further comprising: reaming saidinner channel; and at least partially tapping said inner channel.
 7. Amethod as in claim 1 further comprising: inserting a replacementfastener in a hole of the structure; and riveting said replacementfastener to said structure.
 8. A method as in claim 1 furthercomprising: determining thickness of a protruding portion of the rivetedfastener extending through the structure; comparing said thickness witha predetermined thickness; and at least partially removing saidprotruding portion such that said thickness is within a predeterminedrange.
 9. An extraction apparatus for removal of a head of a rivetedfastener comprising: a shaft configured for insertion into the head; anda support member coupled to said shaft and configured for positioningover the head; said shaft separating the head from a structure wheninserted into an inner channel of the head.
 10. An apparatus as in claim9 wherein said shaft comprises a threaded portion that when turned intosaid inner channel pulls the head from said structure.
 11. An apparatusas in claim 9 wherein said shaft is part of a threaded fastener, whichrotates at least partially within said support member.
 12. An apparatusas in claim 9 wherein said support member comprises an inner diameterthat is larger than an outer diameter of the head.